When running under Windows (I'm using XP), if the DPI is set to something besides the standard 96 DPI, the PasswordMaker dialog box gets clipped. (Fortunately, it can be resized, but it's a pain.)
To reproduce, from the Control Panel, click Display Properties. On the Settings tab, click Advanced. In the General tag, change the DPI to 120.
Now, in Firefox, click Tools > PasswordMaker.
You'll see a dialog whose borders are too small for its contents.